int main(int argc, char **argv)
{
TApplication *myApp = new TApplication(“myApp”,&argc,argv);
ifstream in;
Double_t x[1000];
char line[20];
for ( int i = 0; i<100; i++) x[i]=0;
in.open(“dummy.txt”);
Int_t nlines = 0;
TFile *f = new TFile(“basic.root”,“RECREATE”);
while (!in.eof()) {
in.getline(line,255); // read a line of the file
istrstream st(line);
st >> x[nlines] ;
if (!in.good()) break;
if ( nlines < 3 ) {
//x = in.get(); //it doesn work properly !
cout << " x = " << x[nlines] << endl;
nlines++;
}
}
//it prints the number of lines
printf(" found %d lines \n",nlines);
// close the file
in.close();
f->Write();
myApp->Run();
return 0;
}
The first thing that I want to do is to store the data from a file like this (file “dummy.txt”)
Hello: 10
Value: 5
1 2 3 4 5 6 7 8
that is, 2 labelled numbers and an array. In an future I will read this “x” times. I had tried with “in.ignore(6)” for example, to avoid the chain, but I obtain only crap (maybe hexdec values of the letters ?)
You never actually make it clear what your specific problem is,
but there are definitely mistakes in your code, for example the
getline() call can cause a memory overwrite.
Following is some example code which does the i/o part of your
question. Some of the error handling code is commented out
because it provokes a bug in the cint bytecode compiler, but
the commented out code works fine if you compile using ACLiC.
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
void problem()
{
int i;
string s;
vector<int> v;
ifstream infile;
// handle i/o errors by throwing an exception
infile.exceptions(ios_base::badbit | ios_base::failbit);
infile.open("problem.txt");
// get label and number
infile >> s >> i;
cout << s << " " << i << endl;
// get label and number
infile >> s >> i;
cout << s << " " << i << endl;
//
// now get the array of numbers
//
// Note: We have to take failbit out
// of the exception handling
// because failbit gets set when
// we reach eof, so we must test
// for that condition by hand.
infile.exceptions(ios_base::badbit);
// We must attempt a read before
// checking for eof, it will not be set
// until we try to read.
infile >> i;
while (!infile.eof()) {
// Note: At this point we may have failbit
// set because the next thing in the
// file was not a number.
// This next line is commented out because
// of a bug in the cint bytecode compiler.
// In compiled code it should be used.
//
//if (infile.fail()) throw "integer conversion error";
// remember the number we just read
v.push_back(i);
// try the next read, eofbit will be set when
// we reach the end of the file
infile >> i;
}
infile.close();
// print out the array
cout << "array:";
for (vector<int>::iterator iter = v.begin(); iter != v.end(); ++iter) {
cout << " " << *iter;
}
cout << endl;
}
[quote=“Physlock”]Ok, I’ll test it and I will post here my results!
I have no experience handling exceptions, so, I’ll check this part especially.
Thanks !
8)[/quote]
The exception handling is just a way to exit quickly when an
error occurs without having to check after each i/o statement.
It is not vital to the actual function of the example, but it is a
common programming mistake to not check error codes after
doing an i/o, so I always attempt to include at least minimal
error handling in an example.
